In systems with large board power requirements, a distributed power architecture, using an intermediate bus voltage, tend to become more and more used. The reason behind this approach is the increasing demand for fast load step response in the down-stream DC/DC converters, normally defined as Point-Of-Load, POL converters. In order to obtain a fast load step response, the POL converter is based on a non-isolated structure. Therefore, the Intermediate Bus Converter, IBC, provides isolation between the voltage distribution and the intermediate bus voltage, which is held at a level, appropriate as input voltage for the POL converter. Thus, a key feature for the IBC is conversion efficiency.
Since conversion efficiency of the IBC is a key feature, MOSFETs are used to rectify the transformer's secondary voltage. This method is normally referred to as synchronous rectification. Such a device significantly reduces conduction losses compared to Schottky diodes. The most utilized rectifying method is the “self-driven” structure, where the voltage across the transformers secondary is used as a gate-drive for the synchronous rectifiers. This method is well recognized and described in any power conversion literature.
Unregulated intermediate bus converters (defined as “fixed ratio IBC”) are running with a duty cycle very close to 50% for each half cycle. In order to prevent failure or malfunction, there is a small functional dead-band between the primary switches, which will lead to power losses. Some prior art solutions propose ways of reducing the dead band.
US 2005/0184716 A1 discloses an apparatus for minimizing the power losses associated with the dead time between the on-time of to series connected switches of a power converter. A control arrangement is provided to change the duration of the dead time in order to minimize the power loss.
U.S. Pat. No. 7,184,281 B2 discloses a power converter having a control circuit for minimizing the dead time to reduce the energy loss caused by alternating between the two switches.
However, as mentioned above, the dead band serves the function of preventing failure or malfunction of the circuit. Therefore, the dead band cannot be avoided altogether, without risking failure or malfunction.